The invention relates to a sensor device for a motor vehicle, in particular a sensor device for capacitive detection of approaches of a user to the vehicle.
The sensor device is designed with at least one multi-layer printed circuit board, having numerous metallized planes. A capacitive sensor electrode is formed for detecting purposes on one of the metallized planes. A control device is coupled to the sensor electrode, in order to apply an electric voltage in relation to a reference potential to the sensor electrode. An evaluation device detects capacitance changes at the sensor electrode, in order to detect the approaches of a user to the sensor electrode. The control device and evaluation device can be integrated thereby to form a single device.
Capacitive detection systems for approaches are known in technology. A capacitance is formed between the sensor electrode, which is brought to a predefined potential, and a reference electrode, e.g. the vehicle ground or the ground of the substrate located under the vehicle. This capacitance can vary when a body moves within the sensing range of the sensor assembly, e.g. the foot of a user. The detection of the capacitance itself can be accomplished in a variety of ways. By way of example, a number of clocked discharge sequences, or a discharge time period may be used as a measurement value for the capacitance. By way of example, a capacitive detection of an approach to a vehicle door handle is also known from DE 196 17 038 A1.
DE 10 2012 109 034 A1 discloses, by way of example, a vehicle door handle having an integrated sensor assembly. The sensor assembly uses a multi-layer printed circuit board having a sensor electrode, which is formed by numerous conductor structures in adjacent printed circuit board planes having interlayer connections.
The concept of capacitive approach detection using a sensor electrode, a shielding electrode (also known as a directing electrode) and a reference electrode is likewise known in technology. By way of example, a concept of this type is disclosed in EP 2 568 605. DE 10 2009 002 566 A1 also discloses a sensor assembly having various metallized planes and a sensor electrode as well as a shielding electrode.
Sensor electronics of the specified type are used, for example, to detect the proximity of a hand of the user of a vehicle to the door handle or hatch of a vehicle. If such an approach is detected, e.g., a radio signal dialog is triggered with an access key for the vehicle from a vehicle-side electronics system.
As can be derived from the prior art and the aforementioned documents, the sensor electrode is aimed at the detection area. A shielding electrode is placed on the side facing away from the detection area, wherein the shielding electrode tracks the sensor electrode in terms of its potential, or is varied in relation to the potential thereof. However, the capacitance changes to the sensor electrode are evaluated, not those of the shielding electrode. A ground electrode may be placed behind the shielding electrode, to serve as a reference potential for the capacitance detection.
Modern vehicles and operating systems require increasingly more complex and also more flexible operating possibilities.
The object of the invention is therefore to provide an improved sensor assembly for a capacitive approach detection.